Metal powders are commonly formulated into high energy explosives, solid fuel propellants and pyrotechnics, for military and commercial applications. For example, aluminum metal is a low cost, low density fuel which is typically used in the form of powder or flake.
In high-energy systems, the energy of the blast and the velocity of the detonation wavefront can be limited by the utilization efficiency and oxidation reaction rate of the aluminum powder. This limits the early-time reaction rate and brisance of an aluminized explosive formulation.
In solid fuel propellant formulations, the formation of aluminum oxide reduces the efficiency of the combustion process and lengthens ignition and combustion times. Other negative performance characteristics in aluminized propellants include erosion of motor components by large aluminum oxide droplets, poor combustion efficiency for low motor pressures and small motors, acoustic instabilities, and reduced nozzle thrust efficiency due to thermal and velocity lag of the oxide droplets.
Many of these negative attributes are due to aluminum particle agglomeration, which can promote combustion inefficiencies and slug formation. The reaction rate and completion of the oxidation process are generally higher for finer (1 to 20 .mu.m) aluminum powders. However, the production, handling, storage, and transport of fine powders become significant limitations in the fabrication of energetic formulations. Very fine powders have poor performance in electrostatic discharge tests which precludes their use in many energetic formulations.
Passivation of fine aluminum powders via formation of a thick protective aluminum oxide layer reduces the reactivity and amount of fuel available for reaction. Ideally, very fine aluminum powder is desired which is composed of pure, unoxidized metal which is safe to handle. In a high energy detonation reaction, the very fine powder will increase the early-time reaction rate and brisance of the explosive, and in a solid fuel propellant formulation, it will improve combustion efficiency and reduce aluminum agglomeration. The present invention addresses a nanolaminate composite material which, in addition to its' structural properties, can be comminuted to a metal powder which has very high surface area of virtually unoxidized metal, which burns very efficiently and rapidly at low temperatures with no particle agglomeration.